Space-based surveillance systems use infrared detectors coupled to computerized data processing for monitoring heated objects and their movements. The infrared spectrum covers a wide range of wavelengths, from about 0.75 micrometers to 1 millimeter. The function of infrared detectors is to respond to energy of a wavelength within some particular portion of the infrared region. Heated objects will dissipate thermal energy having characteristic wavelengths within the infrared spectrum. Different levels of thermal energy, corresponding to different sources of heat, are characterized by the emission of signals within different portions of the infrared frequency spectrum. Different levels of thermal energy, corresponding to different sources of heat, are characterized by the emission of signals within different portions of the infrared frequency spectrum. Detectors are selected in accordance with their sensitivity in the range of interest to the designer. Similarly, electronic circuitry that receives and processes the signals from the infrared detectors must also be selected in view of the intended detection function.
Current infrared detection systems incorporate arrays of large numbers of discrete, highly sensitive detector elements the outputs of which are connected to sophisticated processing circuity. By rapidly analyzing the pattern and sequence of detector element excitations, the system circuitry can identify and monitor sources of infrared radiation. The outputs of the detectors must undergo a series of processing steps in order to permit derivation of the desired information. The more fundamental processing steps include preamplification, tuned bandpass filtering, clutter and background rejection, multiplexing and fixed noise pattern suppression. By providing a detector connecting module that performs at least a portion of the signal processing functions within the module, i.e. on integrated circuit chips disposed adjacent the detector focal plane, the signal from each detector need be transmitted only a short distance before processing.
As a consequence of such on-focal-plane or "up front" signal processing, reductions in size, power and cost of the data processor may be achieved. Volume available aboard spacecraft for large data processors is very limited, and launch costs exceed $3,000 per pound. Moreover, up front signal processing helps alleviate performance and reliability problems associated with the construction of millions of closely spaced conductors connecting each detector element to the main signal processing network.
While the concept of a detector connecting module permits on-focal-plane processing, in practice the on-focal-plane processing is limited due to the fact that the algorithms used to select, rate and process incoming data have yet to be finalized. In order to avoid discarding possibly useful data existing modules largely pass the data from millions of detector elements directly to the off-focal-plane processor. In practice, it may be only after years of space-based experience that the algorithms may be finalized.
In view of the inability of the prior art to develop algorithms on the ground before the launch of space-based surveillance, it is desirable to provide a data processing system that may pass through nearly all the data, but may also adapt to process appropriate portions of the data as algorithms evolve.